Geomagnetic Disturbance Index Research Articles

Establishment and Application of an Interplanetary Disturbance Index Based on the Solar Wind–Magnetosphere Energy Coupling Function and the Spectral Whitening Method

We develop a preliminary interplanetary disturbance index (J sW ) by applying the spectral whitening method to an energy coupling function with solar wind measurements during the years 1998–2014 as the input, which can be used as an indicator of perturbations in the near-Earth solar wind. The correlation and temporal variation between J sW and the geomagnetic disturbance index (J pG ) constructed from the same method have been analyzed in detail for 167 geomagnetic storms with the minimum D st index less than or equal to −50 nT. The time delay between J sW and J pG is clearly observable and varies for different events, according to which J sW is shifted backward with respect to J pG . We obtain a fairly good negative correlation between the shifted J sW and the J pG indices for the majority of events, and the significance level for 88% of the events (i.e., 147 events) does not exceed 0.05. A statistical analysis of the shifted J sW and the J pG indices for 147 selected events reveals that larger values of J sW and smaller magnitudes of J pG are commonly accompanied by enhanced southward magnetic fields, which implies that more solar wind energy is entering the magnetosphere and thus causing strong geomagnetic storms. Furthermore, a linear fit of the two indices suggests that the evolution of J pG can be predicted about 2 hr in advance based on J sW , indicating that J sW can provide early warnings of possible disturbances in the geomagnetic fields, which is crucial for space weather monitoring and operational forecasting.

Biotropic effects of geomagnetic disturbance in middle latitudes: psychological aspects of the problem

Objective. To identify the individual psychological features and forms of stress coping in volunteers, participating in one of the stages of latitudinal monitoring Geliomed and living in the middle latitudes depending on the presence of psychological sensitivity to the impact of geomagnetic disturbance. Materials and methods. Fifty-seven rather healthy male and female volunteers (mean age 42.3 (39.6; 47.5) years), living in the middle latitudes (Saratov city) were examined using the Spielberger Hanin Anxiety Test, the Haim Stress Coping Behavior Test and projective psychogeometrical test. Based on matching pick values of reactive anxiety and Kr-index (integral geomagnetic disturbance index), all volunteers were divided into two groups: group I those having psychological sensitivity to the impact of heliogeomagnetic factors and group II without the latter. Results. The standard personal features of the observed persons were found to depend on the presence or absence of psychological sensitivity to the changes in geomagnetic disturbance and are reflected in the peculiar features of the stress-coping behavior formed by them. The volunteers of group I were less effective in the behavior sphere, they more often analyzed problems and suppressed their emotions compared with those of group II. Conclusions. Thus, the persons having psychological sensitivity to the changes in geomagnetic disturbance require psychological correction of the established changes to decrease risk for the development of neuroses and psychological pathology.

A New Index to Describe the Response of Geomagnetic Disturbance to the Energy Injection from the Solar Wind

In this paper, we establish a new non-dimensional global geomagnetic disturbance index JpG by applying the spectral whitening method to the horizontal components of geomagnetic fields observed at eight ground-based stations distributed at low and middle latitudes during years 1998 to 2014. This index can describe the development of geomagnetic storms and its relationship with the Dst index has been verified, which gives a correlation coefficient (CC) of about 0.72. We also check the response of JpG to the arrival of upstream solar wind energy based on a proxy that the ring current injection term Q. The variation of JpG in course of geomagnetic storms is similar to the variation of Q, and the recorded minimum values of Q (Qmin) and JpG (JpGmin) for 30 great storms yields a relatively better CC of about 0.82. These results illustrate that JpG can effectively depict the storm evolution and is well related to the associated Q in amplitude, which provides an alternative means of geomagnetic storm forecasting. In addition, we note that the time difference between Qmin and JpGmin, as well as the time difference when JpG recovers from JpGmin to half and/or one-third of its value, are shorter than those of the corresponding Dst index. And especially, for multiple storms that occurred continuously on a short time scale, the recovery of the Dst index to a quiet period level can be affected by the following solar wind energy input, while the JpG index does not and exhibits independently.

Investigation of two coronal mass ejections from circular ribbon source region:Origin, Sun-Earth propagation and Geoeffectiveness

In this article, we compare the properties of two coronal mass ejections (CMEs) that show similar source region characteristics but different evolutionary behaviors in the later phases. We discuss the two events in terms of their near-Sun characteristics, interplanetary evolution and geoeffectiveness. We carefully analyzed the initiation and propagation parameters of these events to establish the precise CME-interplanetary CME (ICME) connection and their near-Earth consequences. The first event is associated with poor geomagnetic storm disturbance index (Dst ≈-20 nT) while the second event is associated with an intense geomagnetic storm of DST ≈-119 nT. The configuration of the sunspots in the active regions and their evolution are observed by Helioseismic and Magnetic Imager (HMI). For source region imaging, we rely on data obtained from Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO) and Hα filtergrams from the Solar Tower Telescope at Aryabhatta Research Institute of Observational Sciences (ARIES). For both the CMEs, flux rope eruptions from the source region triggered flares of similar intensities (≈M1). At the solar source region of the eruptions,we observed a circular ribbon flare (CRF) for both cases, suggesting fan-spine magnetic configuration in the active region corona. The multi-channel SDO observations confirm that the eruptive flares and subsequent CMEs were intimately related to the filament eruption. Within the Large Angle and Spectrometric Coronograph (LASCO) field of view (FOV) thetwo CMEs propagated with linear speeds of 671 and 631 km s−1, respectively. These CMEs were tracked up to the Earth by Solar Terrestrial Relations Observatory (STEREO) instruments. We find that the source region evolution of CMEs, guided by the large-scale coronal magnetic field configuration, along with near-Sun propagation characteristics, such as CME-CME interactions, played important roles in deciding the evolution of CMEs in the interplanetary medium and subsequently their geoeffectiveness.

The Variation of Geomagnetic Storm Duration with Intensity

Variability in the near-Earth solar wind conditions can adversely affect a number of ground- and space-based technologies. Such space-weather impacts on ground infrastructure are expected to increase primarily with geomagnetic storm intensity, but also storm duration, through time-integrated effects. Forecasting storm duration is also necessary for scheduling the resumption of safe operating of affected infrastructure. It is therefore important to understand the degree to which storm intensity and duration are correlated. The long-running, global geomagnetic disturbance index, mathit{aa}, has recently been recalibrated to account for the geographic distribution of the component stations. We use this mathit{aa}_{H} index to analyse the relationship between geomagnetic storm intensity and storm duration over the past 150 years, further adding to our understanding of the climatology of geomagnetic activity. Defining storms using a peak-above-threshold approach, we find that more intense storms have longer durations, as expected, though the relationship is nonlinear. The distribution of durations for a given intensity is found to be approximately log-normal. On this basis, we provide a method to probabilistically predict storm duration given peak intensity, and test this against the mathit{aa}_{H} dataset. By considering the average profile of storms with a superposed-epoch analysis, we show that activity becomes less recurrent on the 27-day timescale with increasing intensity. This change in the dominant physical driver, and hence average profile, of geomagnetic activity with increasing threshold is likely the reason for the nonlinear behaviour of storm duration.

Harmonic Analysis of Ionospheric Total Electron Content (TEC) Using Kalman Filter

The ionospheric diurnal variation from TEC Global Ionospheric Maps (GIM) data at the epicenter coordinates of the Lombok earthquake on July 29 2018 (-8.4°, 116.5°) has been analyzed using harmonic function which is the sum of the sine and cosine functions with estimated harmonic coefficients obtained using Kalman Filter (KF) method. The initial value of the estimated KF method was obtained from Least Square Estimation (LSE) on the first day data. The estimated TEC value by the KF method shows that there are seasonal variations of the peak values of diurnal variations which is a result of variation in the zenith angle of the sun that change over a year with peaks in March and November in the equator. The results of the first-order harmonic amplitude analysis, namely the diurnal TEC variation (A24) which is the root value of the sum of the squared values of the A1 and B1 coefficients were further analyzed by estimating polynomials with order 17 to eliminate the seasonal effect on A24. The difference in value of A24 from its estimation with order 17 polynomial (delta A24) shows the influence of geomagnetic and seismic activity. A24 analysis based on solar radiation flux at wavelength 10.7 cm (F10.7) does not indicate a strong influence or relationship> Equatorial geomagnetic disturbance index (etc.) shows the influence of geomagnetic storms on diurnal amplitude and earthquake data around Lombok indicating symptoms of pre-earthquake that affects the ionospheric TEC through a decrease in diurnal amplitude a few days before the earthquake.

Linear time-series modeling of the GNSS based TEC variations over Southwest Japan during 2011–2018 and comparison against ARMA and GIM models

A significant amount of research has been conducted in Southwest (SW) Japan on climate modeling, disaster management, earthquake prediction, precise positioning, datum definition, and reference frames. However, there is substantial scope for numerical modeling and forecasting of ionospheric Total Electron Content (TEC) variations over the region, which would be beneficial for further communication and navigation purposes. Therefore, in this study we examined spatio-temporal ionospheric TEC variations using long-term Global Navigation Satellite System (GNSS) measurements from 01 January, 2011 to 31 December, 2018 through a modified Linear Time-series Model (LTM) and substantiated our findings by comparing them with those of the existing empirical Global Ionospheric Map (GIM) and Auto-Regressive Moving Average (ARMA) methods. We analyzed TEC variations at 10 permanent stations covering three districts of SW Japan, which mainly include the Kyushu district and parts of the Chugoku and Shikoku districts. To determine the performance of the LTM, the geomagnetic (Northern Polar Cap (PCN) and Disturbance (Dst)) indices were included, together with the additional solar and planetary geomagnetic disturbance indices (F10.7 and Ap). Our comparison results show that the Root Mean Square Error (RMSE) values in terms of TEC units (TECUs) between the observed and the TEC predicted by the LTM vary from 1.57 to 1.66, which are better than those between the observed and the TEC predicted by the ARMA (1.84–1.93) and the GIM (9.67–9.84) TEC models. An analysis of the results emphasizes the superior performance of the LTM over the other models in terms of its discriminability of temporal, as well as spatial, components.

Correlation between the Lunar Phase and Tail-Lifting Behavior of Lizards (Pogona vitticeps) Exposed to an Extremely Low-Frequency Electromagnetic Field.

Simple SummaryWe examined the relationship between the number of tail lifts of lizards (Pogona vitticeps) and environmental factors, such as the calendar month, daily mean temperature, daily mean humidity, daily mean atmospheric pressure, lunar phase (full moon/new moon), and K index as a geomagnetic disturbance index using 16 months of data. We set up an extremely low-frequency electromagnetic field (ELF-EMF) group and a control group. In a multiple linear regression analysis, the independent determinants associated with the number of tail lifts were the full moon, the temperature, February, March, April, and May in the ELF-EMF group and March, April, May, and June in the control group. The P. vitticeps in the ELF-EMF group responded to the full moon whereas those in the control group did not.We previously showed that the agamid lizard Pogona vitticeps responded to an extremely low-frequency electromagnetic field (ELF-EMF; frequency: 6 and 8 Hz; peak magnetic field: 2.6 µT; peak electric field: 10 V/m) with tail-lifting behavior. In addition, the tail-lifting response to ELF-EMF disappeared when the parietal eyes of the lizards were covered by small round aluminum caps. This result suggests that the parietal eye contributes to light-dependent magnetoreception. In the present study, we set up an ELF-EMF group to evaluate the long-term effect of the ELF-EMF on lizards’ behavior and examine our hypothesis that exposure to ELF-EMFs increases the magnetic field sensitivity in lizards. We therefore include the lunar phase (full moon/new moon) and K index as environmental factors related to the geomagnetic field in the analysis. The number of tail lifts per individual per day was the response variable while calendar month, daily mean temperature, daily mean humidity, daily mean atmospheric pressure, full moon, new moon, and K index were the explanatory variables. We analyzed an ELF-EMF group and a control group separately. In a multiple linear regression analysis, the independent determinants associated with the number of tail lifts were the full moon, the temperature, February, March, April, and May in the ELF-EMF group and March, April, May, and June in the control group. The P. vitticeps in the ELF-EMF group responded to the full moon whereas those in the control group did not. In addition, in the ELF-EMF group, the number of tail lifts was higher on days when the K index was higher (P = 0.07) in the first period whereas there was no such tendency in either period in the control group. There is the possibility that the exposure to ELF-EMFs may increase magnetic-field sensitivity in lizards.

Impact of heliogeophysical factors on the clinical-biochemical indices in pregnant women

<p>The influence of heliogeophysical factors on the clinical and biochemical parameters of pregnant women with easy and complicated births was studied. The influence of the events of the current day and the previous solar and geomagnetic activity on clinical and biochemical parameters of pregnant women with normal and complicated births was revealed. 164 pregnant women aged from 17 to 44 years, living in Barnaul, Altai region, were examined. According to the type of delivery two groups of women were identified:1) women with easy birth (46 people), 2) women with complicated birth (118 people). The following indicators were used to estimate the level of solar and geomagnetic activity: the number of sunspots, the number of Wolff, radiation at a wavelength of 10.7 cm, the average daily magnetic field perturbation (A<sub>p</sub>– index), and the local geomagnetic disturbance index (A<sub>k </sub>– index). Pregnant women were examined using the following parameters: the number of erythrocytes, leukocytes, blood platelets, leukocyte count, clotting time, erythrocyte sedimentation rate, prothrombin index, hemoglobin, sugar, fibrinogen, bilirubin (direct, indirect and total), total blood protein, and specific gravity. It has been established that the influence of heliogeophysical factors consists of immediate and delayed reactions with different latent periods: among women with normal births the most significant events are the events of the current day, as well as the 3rd, 6th and 7th days before the examination; among women with difficult births - on the 2nd, 4th, 5th and 7th days. Among heliogeophysical factors the average daily disturbance of the Earth's magnetic field has the greatest influence on clinical and biochemical parameters. 60% of the clinical and biochemical parameters analyzed among pregnant women depend on this factor. Clinical and biochemical indicators are less susceptible to heliogeophysical factors among women with complicated births. The coefficient of determination by the factors of solar activity reaches 25% (direct bilirubin) among them; factors of geomagnetic activity - 31.5% (urine protein), whereas in the group of women with normal births the coefficient of determination is 50% (total bilirubin) and 71% (total bilirubin). According to clinical-biochemical indicators 8 types of correlations were found: 1 type – at low level of solar and geomagnetic activity, 4 types – at medium and 3 types at high level. Linear and nonlinear functional dependencies of the indicators on heliogeophysical factors are revealed for each typological group.</p>

Comparison of planetary and local geomagnetic disturbance indices: Operational implications

Geomagnetic storms can disrupt social infrastructure on Earth; thus, accurate and timely monitoring is required to reduce their future socioeconomic impact. This study compares the planetary geomagnetic disturbance index (KP) with local indices at Fredericksburg (FRD) and Kakioka (KAK) stations. Local K indices at KAK and Cheongyang (CYG) are estimated and validated using indices observed at both stations. We found generally similar correlations between the KP index and the local K indices at FRD and KAK; however, their details differ. The results show that, even when planetary geomagnetic storms are observed, the local K can be smaller than the observed KP. This implies that both KP and local K should be simultaneously monitored. Real-time estimation of local K shows that the estimated K at KAK and CYG correlates well with the observed K. The estimation probability at KAK and CYG, with an error range of ±1, is greater than 98% when the local K is greater than 3. This suggests that the estimation approach used in this study can be operationally applied for timely monitoring of local geomagnetic disturbances.

The Electric Storm of November 1882

AbstractIn November 1882, an intense magnetic storm related to a large sunspot group caused widespread interference to telegraph and telephone systems and provided spectacular and unusual auroral displays. The (ring current) storm time disturbance index for this storm reached maximum −Dst ≈ 386 nT, comparable to Halloween storm of 29–31 October 2003, but from 17 to 20 November the aa midlatitude geomagnetic disturbance index averaged 214.25 nT, the highest 4 day level of disturbance since the beginning of aa index in 1868. This storm contributed to scientists' understanding of the reality of solar‐terrestrial interaction. Past occurrences of magnetic storms, like that of November 1882, can inform modern evaluations of the deleterious effects that a magnetic superstorm might have on technological systems of importance to society.

Trend of major earthquakes during the period 1900–2011 and its association with some solar and geomagnetic parameters

The paper presents long term trend of major earthquake (magnitude ≥6 Richter scale) occurrence throughout world. Analysis shows that occurrence trend decreases during the period 1900–1962, afterwards the trend increases. Solar coronal index, geomagnetic disturbance indices (Kp, Ap index) follow the opposite trend during the above mentioned period. Possible explanation is presented.

Study of High Energy Cosmic Ray Anisotropies with Solar<i> </i>and Geomagnetic Disturbance Index

An inter-comparison of the first two harmonics has been made so as to understand the basic reason for the occurrence of cosmic ray anisotropies during the period 1989-2004 and 1991 – 2004 using the Neutron monitor data from and Haleakala Neutron Monitoring Stations. The annual average values of the first two (daily) harmonic amplitudes and phases for neutron monitor data due to the change in the annual average magnitudes of the sunspot number and Ap index. Significant positive correlations among diurnal amplitude of both stations with <i>Rz</i> and <i>Ap</i> index have been found. The largest amplitudes are observed during the declining phase of solar activity. The semi-diurnal amplitude for Kiel and Haleakala neutron monitor stations have been found negatively correlated with sunspot number and <i>Ap</i> index, while the semi-diurnal phase is positively correlated with sunspot number and <i>Ap </i>index.Examinations and analysis of simultaneous variations in cosmic ray anisotropies along with solar and geomagnetic disturbance index has lead us to identify possible mechanism in producing significant correlations.

A short-term ionospheric forecasting empirical regional model (IFERM) to predict the critical frequency of the F2 layer during moderate, disturbed, and very disturbed geomagnetic conditions over the European area

Abstract. A short-term ionospheric forecasting empirical regional model (IFERM) has been developed to predict the state of the critical frequency of the F2 layer (foF2) under different geomagnetic conditions. IFERM is based on 13 short term ionospheric forecasting empirical local models (IFELM) developed to predict foF2 at 13 ionospheric observatories scattered around the European area. The forecasting procedures were developed by taking into account, hourly measurements of foF2, hourly quiet-time reference values of foF2 (foF2QT), and the hourly time-weighted accumulation series derived from the geomagnetic planetary index ap, (ap(τ)), for each observatory. Under the assumption that the ionospheric disturbance index ln(foF2/foF2QT) is correlated to the integrated geomagnetic disturbance index ap(τ), a set of statistically significant regression coefficients were established for each observatory, over 12 months, over 24 h, and under 3 different ranges of geomagnetic activity. This data was then used as input to compute short-term ionospheric forecasting of foF2 at the 13 local stations under consideration. The empirical storm-time ionospheric correction model (STORM) was used to predict foF2 in two different ways: scaling both the hourly median prediction provided by IRI (STORM_foF2MED,IRI model), and the foF2QT values (STORM_foF2QT model) from each local station. The comparison between the performance of STORM_foF2MED,IRI, STORM_foF2QT, IFELM, and the foF2QT values, was made on the basis of root mean square deviation (r.m.s.) for a large number of periods characterized by moderate, disturbed, and very disturbed geomagnetic activity. The results showed that the 13 IFELM perform much better than STORM_foF2,sub&gt;MED,IRI and STORM_foF2QT especially in the eastern part of the European area during the summer months (May, June, July, and August) and equinoctial months (March, April, September, and October) under disturbed and very disturbed geomagnetic conditions, respectively. The performance of IFELM is also very good in the western and central part of the Europe during the summer months under disturbed geomagnetic conditions. STORM_foF2MED,IRI performs particularly well in central Europe during the equinoctial months under moderate geomagnetic conditions and during the summer months under very disturbed geomagnetic conditions. The forecasting maps generated by IFERM on the basis of the results provided by the 13 IFELM, show very large areas located at middle-high and high latitudes where the foF2 predictions quite faithfully match the foF2 measurements, and consequently IFERM can be used for generating short-term forecasting maps of foF2 (up to 3 h ahead) over the European area.

Assessing the validity of station location assumptions made in the calculation of the Geomagnetic Disturbance Index,Dst

In this paper, the effects of the assumptions made in the calculation of the Dst index with regard to longitude sampling, hemisphere bias, and latitude correction are explored. The insights gained from this study will allow operational users to better understand the local implications of the Dst index and will lead to future index formulations that are more physically motivated. We recompute the index using 12 longitudinally spaced low-latitude stations, including the traditional 4 (in Honolulu, Kakioka, San Juan, and Hermanus), and compare it to the standard United States Geological Survey definitive Dst. We look at the hemisphere balance by comparing stations at equal geomagnetic latitudes in the Northern and Southern hemispheres. We further separate the 12-station time series into two hemispheric indices and find that there are measurable differences in the traditional Dst formulation due to the undersampling of the Southern Hemisphere in comparison with the Northern Hemisphere. To analyze the effect of latitude correction, we plot latitudinal variation in a disturbance observed during the year 2005 using two separate longitudinal observatory chains. We separate these by activity level and find that while the traditional cosine form fits the latitudinal distributions well for low levels of activity, at higher levels of disturbance the cosine form does not fit the observed variation. This suggests that the traditional latitude scaling is insufficient during active times. The effect of the Northern Hemisphere bias and the inadequate latitude scaling is such that the standard correction underestimates the true disturbance by 10–30 nT for storms of main phase magnitude deviation greater than 150 nT in the traditional Dst index.

Statistical Analysis of Geomagnetic Disturbances and Ionospheric Scintillations Over Guangzhou Region During Solar Minimum

基于肇庆地磁台的地磁监测数据和广州气象卫星地面站建立的华南地区GPS电离层闪烁监测网的监测数据, 统计分析了2008年7月至2010年7月太阳活动低年期间广州地区地磁扰动与电离层闪烁的关系. 用肇庆台地磁水平分量<I>H</I>的变化量换算出肇庆地磁指数<I>K</I>, 以此来代表广州地区地磁扰动情况.分析结果表明, 磁暴/强地磁扰动对广州地区电离层闪烁的发生总体表现为抑制作用, 电离层闪烁主要发生在低<I>K</I>值期间, 而在<I>K</I> ≥ 4时电离层闪烁的发生呈下降趋势. 电离层闪烁发生率随季节和地磁活动的变化规律表现在, 春季的弱闪烁发生率、夜间中等以上闪烁发生率和夏季中等以上闪烁的发生率明显与地磁活动指数<I>K</I>相关, 即随$K$指数的增大而减小; 在秋季和冬季闪烁发生率与<I>K</I>指数变化无明显关系. 同时还综合分析了地磁与太阳活动的变化对电离层活动的影响, 广州地区闪烁主要发生在太阳活动较低的磁静日期间.

Effect of solar activity and geophysical disturbance on physical-chemical processes in liquid medium: Preliminary analysis of storm-glass activity

Changes in the state of a solution in storm glasses (Fitzroy retort) have been recorded by measuring the height of the level of crystals. Devices manufactured by a group of Crimean researchers have been used to measure these characteristics daily since 1995. Fragments of an accumulated observation dataset have been processed employing standard meteorological and cosmophysical indices. It is found that, 2–3 days before isolated sharp drops in the atmospheric pressure, crystal formation intensifies synchronously in two devices. A relationship is found between the activity under study and changes in the Ap geomagnetic-disturbance index and the flare-intensity index. There is a set of quasi-stable periods in variations of the activity of storm glasses, of which the 120-, 185-, and 360-day periods are most significant. The obtained results are generally consistent with views that changes in the background electromagnetic low-frequency fields are a physical agent influencing the process of crystal formation.

Geomagnetic storms and the occurrence of phase slips in the reception of GPS signals

We have investigated a dependence of the relative density of GPS phase slips on the geomagnetic disturbance level. The study is based on using Internet-available selected data from the global GPS network, with the simultaneously handled number of receiving stations ranging from 160 to 323. The analysis used four days from the period 1999-2000, with the values of the geomagnetic field disturbance index Dst from 5 to – 300 nT. During strong magnetic storms, the relative density of phase slips on mid-latitudes exceeds that for magnetically quiet days by one-two orders of magnitude as a minimum, and reaches a few percent of the total density of observations. Furthermore, the level of phase slips for the GPS satellites located on the sunward side of the Earth was by a factor of 5-10 larger compared with the opposite side of the Earth. The level of slips of L1 phase measurements at the fundamental GPS frequency is at least one order of magnitude lower than that in L1 – L2 measurements. The slips of L1 – L2 measurements are most likely to be caused by the high level of slips of L2 phase measurements at the auxiliary frequency. As an alternative, we developed and tested a new method for determining TEC variations using only data on the pseudo-range and phase measurements at fundamental frequency L1. The standard deviation of the TEC variations which were obtained in phase measurements at two frequencies, L 1 – L 2 , and at fundamental frequency L 1 , does not exceed 0.1 TECU, which permits this method to be used in strong disturbance conditions when phase slips at auxiliary frequency L2 are observed.

Study of the long‐term variability of interplanetary plasma and fields as a link for solar‐terrestrial relationships

Often the interplanetary parameters used for the study of solar‐terrestrial relationships are solar wind speed (V), the total interplanetary magnetic field (B), and the southward component of IMF (Bz). Both hourly and daily values of these parameters have usually been employed to associate with parameters defining terrestrial effects. For our study, we have used the daily values of the interplanetary indices (V, B, and Bz), as well as the daily values of the geomagnetic disturbance index Ap, for the years 1965–2007. The long‐term averages have been calculated for the days when simultaneous data are available for all the four parameters (V, B, Bz, and Ap). These include their yearly averages, as well as the averages on the basis of the phases of the solar activity cycle. The statistical relationship between them has been investigated on these long‐term averages, as well as on the day‐to‐day basis. These sets have been further divided and studied on the basis of days with Bz being &lt;0 or ≥0. The results obtained can be summarized as follows: (1) the magnitudes of the values of Ap are observed to be always enhanced significantly for the case of Bz &lt; 0, as compared to days with Bz ≥ 0, and (2) V versus Ap has always low values of correlation coefficient (r). (3) On the contrary, B versus Ap has high values of “r”; (4) the product of V and B versus Ap always yields much better correlations than for V or B alone, either on an average basis or on a day‐to‐day basis, and (5) although, the long‐term variations of V are not very significant, the variations of B follow solar activity cycle and has a continuously increasing trend during the solar cycles 20 and 21. The statistical results obtained here signify that the product of V and B is more significantly effective in producing large‐scale geomagnetic disturbances.

A Preliminary Estimate of the Size of the Coming Solar Cycle 24, based on Ohl’s Precursor Method

For many purposes (e.g., satellite drag, operation of power grids on Earth, and satellite communication systems), predictions of the strength of a solar cycle are needed. Predictions are made by using different methods, depending upon the characteristics of sunspot cycles. However, the method most successful seems to be the precursor method by Ohl and his group, in which the geomagnetic activity in the declining phase of a sunspot cycle is found to be well correlated with the sunspot maximum of the next cycle. In the present communication, the method is illustrated by plotting the 12-month running means aa(min ) of the geomagnetic disturbance index aa near sunspot minimum versus the 12-month running means of the sunspot number Rz near sunspot maximum [aa(min ) versus Rz(max )], using data for sunspot cycles 9 – 18 to predict the Rz(max ) of cycle 19, using data for cycles 9 – 19 to predict Rz(max ) of cycle 20, and so on, and finally using data for cycles 9 – 23 to predict Rz(max ) of cycle 24, which is expected to occur in 2011 – 2012. The correlations were good (∼+0.90) and our preliminary predicted Rz(max ) for cycle 24 is 142±24, though this can be regarded as an upper limit, since there are indications that solar minimum may occur as late as March 2008. (Some workers have reported that the aa values before 1957 would have an error of 3 nT; if true, the revised estimate would be 124±26.) This result of the precursor method is compared with several other predictions of cycle 24, which are in a very wide range (50 – 200), so that whatever may be the final observed value, some method or other will be discredited, as happened in the case of cycle 23.